Influence of oxygen content and surface condition on weld quality of pipeline steels

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Welded pipeline steels made of 316 or 316L grade stainless steels are widely used in oil and gas industry mainly for the transportation of very corrosive substances. One of the main challenges in welding of these steels is the occurrence of discoloration of the weld region which results often in the rejection of the part. While the industrial practice is based on AWS D18.2 standard; however, the acceptable level of oxygen is not identified and often a weld, which might be good, is rejected because of apparent discoloration. Recent research has indicated that oxygen trapping by the fusion zone is the main source for the discoloration phenomenon. However, the influence of the oxygen level present during welding on the extent of discoloration and level of damage to the microstructure have not been quantified yet. The objective of the present project is to study the influence of oxygen content and surface condition on the extent of discoloration and their impacts on microstructural changes and mechanical properties of 316 and 316L pipeline steels. The generation of these data is a key element in the selection of the appropriate equipment and process conditions for field application by the industrial partner.